虚拟语气：表示主观愿望和假想虚拟的情况，是通过特殊的谓语动词形式来表达的愿望、假设、怀疑、猜测或建议等语气，它不表示客观存在。
一、虚拟语气用在非真实条件句中
3、在正式文件中，有时省略if，而将were, had, should 提到主语之前（位于句首），表达意思仍与if 条件句相同。
Had it not been for your help, we would not have achieved so much.
二、虚拟语气用在名词性从句中
虚拟语气用在表示要求、建议、命令等名词从句中，从句谓语用“(should)+动词原形”。 1、用在动词insist坚持，suggest建议,order命令，propose建议，demand要求，request, require 等后面的宾语从句中 he suggested that we (should) start now.
如果上述动词不表示主张、建议等意义，仍用陈述语气。
the expression on his face suggests that he knows it.(表明、暗示） 2、用在名词 insistence 坚持, suggestion建议，order命令,proposal建议,demand要求, request, requirement 等后的表语从句和同位语从句。 The proposal is that their output (should) be increased by 2 percent.
3、用在it+ be + adj (natural, necessary, strange, important等)+ that 引导的主语从句结构中
It’s necessary that you should be present at the meeting.
4、在It +be + insisted, suggested，ordered…+that引导的主语从句的结构中。
It was suggested that the medicine should be sent there by plane.
三、用在wish后的宾语从句中 （1）现在:wish + that+主语+过去式
（2）将来: wish + that+主语+would ,might +动词原形 （3）过去:wish + that+主语+ had+过去分词 I wish I knew the answer.
It’s wished that he had not made the mistake.
四、其他
As if, as though （好像）引导的从句中，和wish宾语从句中的形式相同。
They are talking as if they had been old friends. 本句型有时用陈述语气表示较大真实性。 It looks as if it is going to rain.
If only引导的感叹句
在It’s (about, high) time that …结构中，表示该干某事了，从句谓语动词用过去式。
It’s time that we went to bed.
虚拟语气表示祝愿： 1、用动词原形
long live the friendship! 友谊万岁！ 2、may + 动词原形 may you be happy! 祝你快乐！
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